Starquakes Viewed by Spacecraft Hold Secrets of Stellar Evolution

When looking at stars, COROT is able to detect starquakes, acoustical waves generated deep inside a star that send ripples across a star's surface, altering its brightness. The exact nature of the ripples can allow astronomers to calculate the star's mass, age and even chemical composition.Credit: CNES

A NASA spacecraft
designed to seek out alien worlds has also revealed new details about
the structure and evolution of stars, and should help astronomers
better understand the future of our own sun, researchers announced
today (Oct. 26).

Researchers measured
so-called "starquakes,"
observing oscillations in the brightness of thousands of stars in
much the same way geologists study earthquakes to probe our planet's
interior. NASA's planet-hunting Kepler spacecraft served as their
tool.

The method, called
asteroseismology,
is helping astronomers characterize stars as never before,
researchers said during a news conference at Aarhus University in
Denmark.

"We are just
about to enter a new area in stellar astrophysics," Thomas
Kallinger, of the University of British Columbia and the University
of Vienna, said in a statement. "Kepler provides us with data of
such good quality that they will change our view of how
stars work in detail."

Kepler: A
multipurpose instrument

NASA launched the
Kepler spacecraft in March 2009 with a primary mission of finding
Earth-like alien planets.

So far, it has
identified at least 700
"candidate stars" that could
harbor alien worlds.But researchers are also using the
spacecraft to analyze the stars such planets may be circling.

"Our knowledge
of the planets Kepler discovers is only as good as our knowledge of
the stars that they orbit," said Kepler mission co-investigator
Natalie Batalha, of San Jose State, during the news conference.

As an example of
what asteroseismology can reveal, the researchers offered up a star
called KIC 11026764.

By studying its
pulses, astronomers have learned more about this star than they know
about virtually any star in the universe aside from our sun.

Researchers
determined, for example, that KIC 11026764 is 5.94 billion years old
and is roughly twice the size of our sun. KIC 11026764 will continue
to grow, eventually transforming into a red giant, researchers said.

Such information,
once gathered for hundreds or thousands of stars, will help
astronomers understand stellar structure and evolution in a general
sense. And it could help scientists evaluate the chances that alien
planets could harbor life, researchers said.

Kepler detects alien
planets by watching for the telltale
dimming in a star's brightness caused when a planet crosses in front
of it from Kepler's vantage point. The amount of dimming reveals how
big the planet is relative to its star  but not its actual size.

So knowing the size
of the star will tell researchers how big its planets are, if it has
any, researchers said. Knowing a star's age and what stage it is at
in its stellar evolution can also help astronomers judge how likely
it is for any alien planets around it to harbor life.

No planets are known
to orbit KIC 11026764, but asteroseismology could theoretically be
applied to stars that host planets, researchers said.

Red giants and
stellar lighthouses, too

Astronomers have
been using Kepler to characterize the structure and life cycle of
1,000 red giants. Later in its life, the sun will one day become one
of these huge, bloated stars.

Researchers also reported on the
star RR Lyrae. It has been studied for more than 100 years as the
first member of an important class of stars used to measure
cosmological distances. The brightness of the star oscillates within
a well-known period of about 13.5 hours, researchers said. Yet during
that period, other small, cyclic changes in amplitude occur 
behavior known as the Blazhko effect.

The effect has puzzled
astronomers for decades, but Kepler data may have yielded a clue to
its origin, researchers said. Kepler observations revealed an
additional oscillation period that had never been previously
detected. The oscillation occurs with a time scale twice as long as
the 13.5-hour period. The Kepler data indicates the doubling is
linked to the Blazhko effect.

"Kepler data ultimately
will give us a better understanding of the future of our sun and the
evolution of our galaxy as a whole," Daniel Huber, of the
University of Sydney, said in a statement.

The Kepler
spacecraft uses a huge digital camera,
known as a photometer, to continuously monitor the brightness of more
than 150,000 stars in its field of view as it orbits the sun. The
research team using the telescope to study stars is an international
collaboration known as the Kepler Asteroseismic Science Consortium.